Estuarine Sediment in the Kickemuit River: Analysis of Raw, Decarbonized, Decarbonated, and Acid-Washed Samples Using XRD, XRF, ICP-OES, DRIFTS, and Raman

Education Level

Undergraduate

Faculty Advisor(s)

Professor Stephen O'Shea

Academic Department(s)

Chemistry

Comments

This research was presented at the 2024 Rhode Island Summer Undergraduate Research Symposium, held on Friday, July 26, at the University of Rhode Island and supported by RI NSF EPSCoR.

Symposium Date

2024

Abstract

The Kickemuit River in Rhode Island is a major freshwater input for Mount Hope Bay estuary, and it is a major source of nutrients notably the limiting organic and inorganic phosphorus forms. Phosphorus on entering the more basic saline waters precipitates and deposits within the estuarine sediment bound to Ca and Fe, becoming ecological locked and recycled in this niche. This study analyzed the concentration of metal ions [Fe, Ca, Mg, Al] and their mineral structures by a suite of spectroscopic instrumentation XRD, XRF, ICP, DRIFT, and Raman within the bay sediment and contrasted this with concentration of water soluble and bound phosphates extracted from the sediment. Segmented (25 cm) core samples (1 M) were collected from six different sites from the Kickemuit and Taunton rivers, and Mount Hope Bay. The segmented samples were dried (100˚C 24hrs), ground, sieved (#20 mesh size), and were heated (550˚C 4hrs) to determine the total organic carbon from loss on ignition and further heated (1000˚C 5hrs) to determine total carbonate content. The release of the different forms of phosphorus upon treatment (water and acid washes) was determined by the ascorbic acid chemical spot test. The samples analyzed by spectroscopic instruments and chemical spot tests were compared to the 1646a NIST reference estuarine sediment standard. XRF scans of whole and treated segmented sieved samples identified the presence and an abundance of Fe, Ca, Si, Mn, Al, and Cu metal ions. Further instrumental XRD analysis identified the acid washed decarbonated sample having a high concentration of bound phosphates in the form of ferric phosphate [FePO4] and apatite [Ca5PO4]. XRD spectra also revealed the abundance of aluminosilicates such as kaolinite [Al2Si2O5(OH)4], gibbsite [Al(OH]3], and feldspars [KAlSi3O8], [NaAlSi3O8], [CaAl2Si2O8]. FT-IR DRIFTS analysis of overlaid comparative spectra from each phase of the sediment treatment and extraction shows loss of sulfate, carbonate, and phosphate ions. Raman spectroscopy indicated that heating the dried sediment to a 1000˚C altered the mineral composition and species. ICP-OES was used to identify the concentration of suspended and water-soluble metals and phosphorus directly within filtered pore water and those extracted from the sediment by either aqueous or acid wash. The latter acid wash being more potent extractant of metals and phosphorus ion.

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